Propelling plasma thrusters forward for spacecraft

Electric propulsion thrusters accelerate ions to propel spacecraft and satellites. The electric fields used in these devices damage their electrodes and neutralizers, limiting their lifespans.

Magnetic nozzle radiofrequency plasma thrusters are a promising alternative. Because these devices transport plasma along magnetic fields, they have no exposed electrodes or neutralizers, prolonging their expected lifespans. However, energy and momentum losses at the plasma source wall cause diminished thrust efficiency.

Nakahama and Takahashi designed and implemented a permanent magnet array in a radiofrequency plasma source. This formed a cusp magnetic field to isolate the plasma from the source wall, which decreased wall losses and enhanced thruster efficiency.

These results are consistent with their previous experimental results, which formed a cusp magnetic field using one upstream and one downstream solenoid. In this work, replacing the upstream solenoid with permanent magnets reduced the consumed electric power while maintaining the enhanced thruster performance, inching magnetic nozzle radiofrequency plasma thrusters closer to practical applications.

“Our experiment demonstrates that the cusp field created by permanent magnets improves the thruster performance,” said author Kazunori Takahashi. “The usage of the permanent magnet can reduce the amount of electricity and solenoid used for the magnetic field generation, which is the critical issue for propulsion device development.”

The authors found that moving the permanent magnet array, comprised of 16 neodymium magnets, alters the location of the cusp. If they placed the cusp closer to the radiofrequency antenna, the force on a downstream target plate increased. Next, they will assess how a plasma thruster with a permanent magnet-array-induced cusp performs in a vacuum chamber that simulates space.

Source: “Effect of a permanent-magnet-induced cusp field on a magnetic nozzle radio frequency plasma thruster,” by Yugo Nakahama and Kazunori Takahashi, AIP Advances (2024). The article can be accessed at https://doi.org/10.1063/5.0186991 .